Enantioselective Synthesis of a Key Intermediate in a New Process for Orlistat Using Asymmetric Hydrogenation and a Grignard Reagent Promoted Lactone Cyclization

A new enantioselective synthesis of Orlistat suitable for large-scale preparation is described. Therein, the first isolated key intermediate (R)-3-hexyl-5,6-dihydro-4-hydroxy-6-undecyl-2H-pyran-2-one (12) is prepared via (a) the asymmetric hydrogenation of methyl 3-oxotetradecanoate to (S)-3-hydroxytetradecanoate (9); (b) the acylation of 9 with 2-bromooctanoyl halide (bromide/chloride) to (R)-3-[(2-bromo-1-oxooctyl)oxy]-tetradecanoic acid methyl ester (11) and finally (c) the tert-butyl magnesium chloride promoted cyclization of 11 to the single enantiomer 12. The single enantiomer intermediate 12, previously published as a mixture of enantiomers 2, has been carried on through several steps to Orlistat (1) without any process changes.